Polycondensation of Urea and Boric Acid to Give Polyborate Ester, a Precursor for Boron Nitride

Abstract

Polycondensations (condensation polymerization) are stepwise reactions between
bifunctional or polyfunctional compoents, with elimination of simple molecules such as water or
alcohol and the formation of macromolecular substances. Polyborate ester , formed by this process,
gives ceramic materials during pyrolysis. Polymer pyrolysis offers an attractive alternative to the
typical high temperature powder processing approach in the fabrication of high-performance
ceramics. This approach might also prove to be useful in the fabrication of fibers, coatings, and
composites. It is within this framework that the present study was undertaken; its aim is the
preparation of boron-containing oligomeric precursors which gives boron nitride after
pyrolysis. The precursor was synthesized by the condensation reaction between boric acid
and urea (or other N-containing reactive multifunctional compounds). The oligomeric precursor
and its pyrolysed products were thoroughly characterized by elemental analysis, IR, NMR,
XRD, Thermal Analysis and Transmission Electron Microscopy(TEM). The elemental analysis
results of the oligomer are---- C-13.40%, H-5.97%, N-32.44% and B-17.09%. X-ray diffraction
and TEM studies showed that boron nitride obtained from this system possess tetragonal structure.